Aqueous solutions of polyurethanes or polyurethane ureas have long been known (cf., for example, Angewandte Chemie, 82 (1970), pages 53 to 55, literature references 4-8, 10a).
The hydrophilic centers incorporated in the known water-soluble polyurethanes or polyurethane ureas may be formed both by salt-like groups, i.e. ionic groups, and also hydrophilic non-ionic groups. The "polyurethane ionomers" include both polyurethanes containing chemically fixed cations, i.e., in particular, chemically incorporated ammonium ions, and also polyurethanes containing chemically fixed anions, i.e., in particular, chemically incorporated sulphonate or carboxylate groups. The non-ionic water-soluble polyurethanes include, in particular, the polyurethanes or polyurethane ureas containing polyethylene oxide chains.
The hitherto known water-soluble polyurethane ionomers are either polyelectrolytes having an ionic group content of greater than 100 milliequivalents per 100 g and extreme hardness, although they are brittle, often hygroscopic and expensive to produce, or more or less elastomeric highly flexible polyurethanes synthesized in the conventional manner from polyesters and/or polyethers. These particular products are soluble in water by virtue of containing polyethylene glycol ether sequences, optionally in combination with ionic groups.
Polyesters containing ionic groups also impart solubility in water to the polyurethanes produced from them. On account of the brittleness thereof when dry and the surface tackiness thereof when moist, the highly ionic products are unsuitable for use as sizes in the textile industry. Products having relatively long polyether sequences are too soft and not smooth enough in feel. Furthermore, although ionic polyester urethanes may be produced having the desired range of mechanical properties, they show a tendency towards hydrolytic degradation in aqueous medium and, for this reason, cannot be regenerated by ultra-filtration. However, regeneratability from the effluents accumulating during desizing is an increasing requirement.
Accordingly, an object of the present invention is to provide water-soluble polyurethane anionomers which are no longer attended by the disadvantages referred to above and which, accordingly, satisfy all the requirements imposed on sizes for the textile industry.